Boron-containing magnesia pellets and method for producing the same

Abstract

The application discloses a boron-containing magnesia pellet and a preparation method thereof, and belongs to the technical field of magnesia pellet production, and is characterized by comprising the following steps: S1, preparing a mixture: mixing boron-magnesium-iron concentrate powder, red mud powder, 69-grade acidic concentrate powder and bentonite according to a certain proportion to prepare the mixture; S2, pretreating the mixture: grinding the mixture; S3, preparing green balls: firstly, adding water into the pretreated mixture, and then performing pelletizing to obtain the green balls; and S4, preparing finished balls: the green balls are firstly subjected to screening and drying, and then subjected to low-temperature roasting, and finally cooled to obtain the boron-containing magnesia pellet. The application can solve the technical problems of high roasting temperature, long roasting time and high energy consumption of the mainstream production process of the existing magnesia pellet.

Description

Technical Field

[0001] This invention relates to the field of magnesium pellet production technology, and in particular to a boron-containing magnesium pellet and its preparation method. Background Technology

[0002] As a crucial raw material for ironmaking, the quality of iron ore pellets directly impacts blast furnace smelting. my country's pellet production primarily focuses on acidic iron ore pellets. While these pellets are high-grade, high-strength, uniform in particle size, and have good permeability, they suffer from inherent defects in high-temperature metallurgical properties. Specifically, under high-temperature reduction conditions, they exhibit a high reduction expansion rate, poor strength and softening properties at high temperatures, and are prone to fracturing and pulverization. These defects severely affect the stable operation of blast furnace smelting and hinder further improvements in blast furnace smelting indicators. In contrast, magnesia-based iron ore pellets possess advantages such as low expansion rate, high high-temperature reduction rate, and good softening properties, making them an important direction for pellet development.

[0003] The current mainstream production process for magnesia pellets involves adding finely ground MgO-containing additives, such as lightly calcined dolomite, serpentine, and lightly calcined magnesia powder, to the pellet blend. These processes play a crucial role in improving the physical and metallurgical properties of the pellets. However, with increasing MgO mass fraction in the pellets, the compressive strength of both preheated and roasted pellets decreases. Furthermore, the MgO content affects the optimal roasting regime. As the MgO content rises, obtaining pellets with compressive strength meeting blast furnace standards requires appropriately increasing the roasting temperature and extending the roasting time. This narrows the suitable roasting temperature and time range for pellet production, hindering industrial operation and output growth. Moreover, increasing the roasting temperature increases energy consumption in pellet production, and high-temperature operation also causes damage to the rotary kiln-chain grate equipment system.

[0004] Some pellet production companies also use alkaline magnetite concentrate with high MgO content to produce magnesium pellets. This preparation method is feasible, but high-magnesium alkaline magnetite resources are becoming increasingly scarce, mining is becoming more difficult, the sources are becoming narrower, and its price is relatively high, resulting in high production costs and poor economic benefits for magnesium pellets, which is not conducive to the large-scale long-term production of magnesium pellets. Summary of the Invention

[0005] This invention addresses the technical problems of high roasting temperature, long roasting time, and high energy consumption in the mainstream production process of magnesium pellets, as well as the economic benefits of the shortage and high cost of high-magnesium basic magnetite concentrate. It provides a boron-containing magnesium pellet and its preparation method.

[0006] The first objective of this invention is to provide a method for preparing boron-containing magnesium pellets, comprising the following steps:

[0007] S1. Preparation of mixture: Boron-magnesium-iron concentrate, red mud powder, grade 69 acid concentrate, and bentonite are mixed in a certain proportion to prepare the mixture;

[0008] S2. Pretreatment of the mixture: The mixture is pretreated using common grinding pretreatment methods;

[0009] S3. Preparation of green pellets: After pretreatment, an appropriate amount of water is added to the mixture, and the mixture is pelletized in a disc pelletizer to obtain green pellets.

[0010] S4. Preparation of finished pellets: The above-mentioned green pellets are successively screened and dried, and then subjected to low-temperature roasting thermal operation process. After preheating and low-temperature roasting, and then cooling, low-cost boron-magnesium ore pellets are obtained.

[0011] In the aforementioned low-cost boron-magnesium ore pellet and its preparation method, the boron-magnesium-iron concentrate is obtained by magnetic separation of boron-magnesium-iron ore. The boron-magnesium-iron concentrate contains high levels of MgO and B2O3, as well as magnetite containing MgO and B2O3. Magnetic separation yields the boron-magnesium-iron concentrate. The main chemical composition of the boron-magnesium-iron concentrate is as follows: TFe content 52%–54%, SiO2 content 4%–5%, MgO content 10%–12%, B2O3 content 5%–6%, Ti content 0.01%–0.03%, and a particle size greater than 74μm.

[0012] In the above-mentioned method for preparing boron-magnesium ore pellets, the red mud powder is red mud, a solid waste product from the Bayer process alumina industry. The main chemical components of the red mud are: TFe content 45%–47%, SiO2 content 3%–4%, MgO content 0.1%–0.4%, Ti content 1.5%–2.5%, and a particle size greater than 35% (74 μm).

[0013] In the above-mentioned method for preparing boron-magnesium ore pellets, the 69-grade acidic concentrate is iron concentrate powder beneficiated from ordinary magnetite. Its main chemical composition indicators are: TFe content 69.2%–69.8%, SiO2 content 1.5%–2.5%, MgO content 0.2%–0.4%, Ti content 0.3%–0.6%, and 74μm particle size greater than 95%.

[0014] In the above-mentioned method for preparing boron-magnesium ore pellets, the bentonite is ordinary sodium bentonite.

[0015] In the above-mentioned method for preparing boron-magnesium ore pellets, the dry basis mass percentages of the prepared mixture are as follows: 8%–9% boron-magnesium-iron concentrate, 3%–4% red mud powder, 86%–88% grade 69 acid concentrate, and 1%–2% bentonite.

[0016] In the above-mentioned method for preparing boron-magnesium ore pellets, the pretreatment of the mixture can be performed using a commonly used grinding pretreatment method, such as ball milling, wet milling, or high-pressure roller milling.

[0017] In the above-mentioned method for preparing boron-magnesium ore pellets, the screening process involves screening out qualified green pellets of 8-16 mm size from the prepared green pellets and then feeding them into a chain grate machine for drying.

[0018] In the above-mentioned method for preparing boron-magnesium ore pellets, the drying process is as follows: the temperature of the fume hood in the drying section of the chain grate is controlled between 100℃ and 550℃, the temperature gradient is 50℃ / min, and the drying time is 9min to 10min.

[0019] In the above-mentioned method for preparing boron-magnesium ore pellets, the low-temperature roasting thermal operation includes a preheating process and a low-temperature roasting process. The preheating process includes: the dried green pellets entering the preheating section of a chain grate machine, with the temperature controlled at 600℃~1050℃, a temperature gradient of 50℃ / min, and a preheating time of 9min~10min.

[0020] In the above-mentioned method for preparing boron-magnesium ore pellets, the low-temperature roasting process is as follows: the pellets, after being dried and preheated by a chain grate machine, enter a rotary kiln for roasting. A low-temperature roasting process is adopted, with the temperature inside the rotary kiln controlled at 1140℃~1190℃, and the roasting time being 25min~30min. This low-temperature roasting process reduces the temperature inside the rotary kiln, saves energy, and reduces high-temperature equipment wear.

[0021] In the above-mentioned method for preparing boron-magnesium ore pellets, the cooling process is as follows: the pellets are cooled in stages on an annular cooler until the temperature meets the requirements for storage or transportation.

[0022] A second objective of this invention is to provide a boron-magnesium ore pellet obtained by the above-described method for preparing boron-magnesium ore pellets.

[0023] Compared with the prior art, the present invention has the following advantages and positive effects:

[0024] 1. According to the raw material blending structure and novel thermal operation process of this invention, a low-temperature roasting thermal operation process is implemented during production. Under low-temperature roasting conditions, this invention improves the metallurgical properties of magnesia pellets, reduces production energy consumption, and saves production costs. Furthermore, the lower roasting temperature reduces ring formation within the rotary kiln, extends the maintenance cycle, reduces damage to the rotary kiln, and lowers maintenance costs. In the raw material blending structure of this invention, a certain proportion of boron-magnesium-iron concentrate is added. This concentrate contains high levels of MgO and B2O3, both of which contribute to improving the performance of the pellets. This invention utilizes the high MgO content in boron-magnesium-iron concentrate, mixing it with ordinary magnetite concentrate to form pellets, thereby increasing the MgO content in the pellets and obtaining magnesia-grade pellets, thus solving the technical problem of low metallurgical performance of ordinary acidic pellets. Furthermore, it utilizes the B2O3 component in the boron-magnesium-iron concentrate to improve the compressive strength and reduce the reduction expansion rate of the magnesia-grade pellets under low-temperature roasting conditions. Simultaneously, the low-temperature roasting thermal operation process of this preparation method effectively solves the technical problem of high energy consumption during pellet production.

[0025] 2. The preparation method of this invention includes the addition of a certain amount of boron-magnesium-iron concentrate, which is a product obtained from boron-iron ore through magnetic separation. Boron-iron ore is a composite mineral containing boron, magnesium, and iron. Abundant boron-iron ore resources exist in Liaoning Province, my country, and it boasts advantages such as large reserves and low cost. Boron-iron concentrate is mainly used in the industrial production of borax, containing Fe2O3, Fe3O4, MgO, and B2O3, and has high utilization value. This invention utilizes its boron- and magnesium-containing characteristics, as well as its cost advantage, as a raw material for the production of magnesia pellets, further reducing the cost of iron-containing raw materials for magnesia pellets.

[0026] 3. This invention further incorporates a coarser-grained economical raw material, red mud powder from aluminum plant solid waste, in a certain proportion to achieve a reasonable combination of coarse and fine particle sizes in the pelletizing concentrate, enhance the affinity of the pelletizing material, and thus improve pelletizing performance. While improving the production and quality of boron-magnesium pellets, it also further enhances the economic benefits of pellet ore. Attached Figure Description

[0027] Figure 1 This is a flowchart of a preferred embodiment of the present invention. Detailed Implementation

[0028] To make the above-mentioned objectives, control system design, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] Please see Figure 1 A low-cost method for preparing boron-magnesium ore pellets, comprising the following steps:

[0030] S1. Preparation of mixture: Boron-magnesium-iron concentrate, red mud powder, grade 69 acid concentrate, and bentonite are mixed in a certain proportion to prepare the mixture;

[0031] S2. Pretreatment of the mixture: The mixture is pretreated using common grinding pretreatment methods;

[0032] S3. Preparation of green pellets: After pretreatment, an appropriate amount of water is added to the mixture, and the mixture is pelletized in a disc pelletizer to obtain green pellets.

[0033] S4. Preparation of finished pellets: The above-mentioned green pellets are successively screened and dried, and then subjected to low-temperature roasting thermal operation process. After preheating and low-temperature roasting, and then cooling, low-cost boron-magnesium ore pellets are obtained.

[0034] The boron-magnesium-iron concentrate used in this embodiment is a product obtained from boron-iron ore through magnetic separation. Boron-iron ore is a complex mineral containing boron, magnesium, and iron. Boron-iron concentrate is mainly used in the industrial production of borax, containing Fe2O3, Fe3O4, MgO, and B2O3, and has high utilization value. The boron-magnesium-iron concentrate contains high levels of MgO and B2O3, which play a role in improving the performance of pellets. The main chemical composition indicators of the boron-magnesium-iron concentrate are: TFe content 52%–54%, SiO2 content 4%–5%, MgO content 10%–12%, B2O3 content 5%–6%, Ti content 0.01%–0.03%, and a particle size greater than 74μm.

[0035] Red mud powder can be obtained from red mud, a solid waste produced in the Bayer process alumina industry. The main chemical components of red mud are: TFe content 45%–47%, SiO2 content 3%–4%, MgO content 0.1%–0.4%, Ti content 1.5%–2.5%, and 74μm particle size greater than 35%.

[0036] Grade 69 acidic concentrate can be used as iron concentrate powder from ordinary magnetite. Its main chemical composition indicators are: TFe content 69.2%~69.8%, SiO2 content 1.5%~2.5%, MgO content 0.2%~0.4%, Ti content 0.3%~0.6%, and 74μm particle size greater than 95%.

[0037] Bentonite can be ordinary sodium bentonite.

[0038] The dry basis mass percentages of the mixture are as follows: 8%–9% boron-magnesium-iron concentrate, 3%–4% red mud powder, 86%–88% grade 69 acid concentrate, and 1%–2% bentonite.

[0039] This embodiment utilizes the high MgO content in boron-magnesium-iron concentrate, mixing it with ordinary magnetite concentrate to form pellets, thereby increasing the MgO content in the pellets and obtaining magnesia-grade pellets, thus solving the technical problem of low metallurgical performance of ordinary pellets. Furthermore, the B2O3 component in the boron-magnesium-iron concentrate is used to improve the compressive strength and reduce the reduction expansion rate of the magnesia-grade pellets under low-temperature roasting conditions, thereby enhancing the metallurgical performance of the magnesia-grade pellets. Simultaneously, the low-temperature roasting thermal operation process of this preparation method reduces production energy consumption, effectively solving the technical problem of high energy consumption in pellet production. Additionally, the lower roasting temperature reduces ring formation in the rotary kiln, extending the maintenance cycle, reducing damage to the rotary kiln, and lowering maintenance costs.

[0040] This invention further incorporates a coarser-grained economical raw material, red mud, a solid waste from aluminum plants, in a certain proportion to achieve a reasonable combination of coarse and fine particle sizes in the pelletizing concentrate. This enhances the affinity of the pelletizing materials, thereby improving pelletizing performance. While improving the quality of boron-containing magnesium pellets, this invention also further enhances the economic benefits of magnesium pellets.

[0041] The specific steps are as follows:

[0042] The main quality indicators of the raw materials used are as follows:

[0043] Table 1 Main Quality Indicators of Raw Materials

[0044]

[0045] The above materials are mixed according to the ore blending scheme in Table 2 below to prepare the mixture:

[0046] Table 2 Raw Material Proportioning Table

[0047] Boron-magnesium-iron concentrate 9 69 grade acidic refined powder 86 Red mud powder 4 Bentonite 1 total 100

[0048] The above mixture is mixed and dried in a dryer, then processed by a grinding mill, and then transported by belt to a pelletizing disc. An appropriate amount of water is added to the disc pelletizer to form green pellets.

[0049] On-site production tests of boron-containing magnesium pellets were conducted using this example scheme. Green pellets in the stable production period were compared with conventional magnesium pellets. The results are shown in Table 3 below.

[0050] Table 3 Comparison of raw bulb indicators

[0051]

[0052] The green pellets are transported to large and small roller screens for screening. Green pellets larger than 16mm and smaller than 8mm are screened out and re-pelletized. The qualified green pellets with a particle size of 8mm to 16mm are then fed into a chain grate machine for drying.

[0053] The drying, preheating, and calcination operations shall be performed according to the following thermal operation process:

[0054] Drying process: The temperature of the fume hood in the drying section of the chain grate machine is controlled between 100℃ and 550℃, with a temperature gradient of 50℃ / min and a drying time of 9 to 10 minutes.

[0055] Preheating process: The dried green pellets enter the preheating section of the chain grate machine. The temperature of the preheating section is controlled at 600℃~1050℃, with a temperature gradient of 50℃ / min and a preheating time of 9min~10min.

[0056] Calcination process: After drying and preheating by the chain grate machine, the pellets are put into the rotary kiln for calcination. The low-temperature calcination thermal regime is adopted, and the temperature in the rotary kiln is controlled at 1140℃~1190℃ for 25min~30min.

[0057] Table 4 shows a comparison of the thermal operating parameters between the boron-containing magnesium pellets and conventional magnesium pellets in this scheme.

[0058] Table 4 Comparison of Key Parameters for Thermal Operation

[0059]

[0060] As can be seen from the above, the temperature of each section of the chain grate hood during the production of boron-magnesium iron ore pellets under this scheme is significantly reduced. Specifically, the temperature of the drying section air box decreases by 17℃, the drying section hood temperature decreases by 32℃, the preheating section air box temperature decreases by 64℃, the preheating section hood temperature decreases by 112℃, the kiln tail temperature decreases by 67℃, and the kiln interior temperature decreases by 63℃. This is because the boron-magnesium iron concentrate contains B2O3 with a low melting point. The liquid phase formed after the B2O3 melts can promote the formation of the high-melting-point magnesium iron olivine liquid phase. A small amount of liquid phase can accelerate the diffusion of crystalline particles inside the pellets, strengthening the consolidation of the pellet ore. It also accelerates the formation of high-melting-point magnesium ferrite, promotes the recrystallization of solid particles and grain growth, which is beneficial to the solid-phase consolidation of the pellets, making the pellet structure dense, the magnetite fully oxidized, and the pellet strength improved (see Table 5 for a comparison of the physicochemical properties of the finished pellets). The low-temperature roasting thermal operation process described in this scheme demonstrates that, on the one hand, adding boron-magnesium-iron concentrate to produce boron-magnesium pellets can reduce energy consumption and lower production costs. On the other hand, the reduced roasting temperature decreases ring formation in the rotary kiln, extending the maintenance cycle, reducing damage to the rotary kiln, and simultaneously lowering maintenance costs.

[0061] Table 5 Comparison of Physicochemical Properties of Finished Pellets

[0062] Conventional magnesium pellets 2372 95.79 Boron-magnesium pellets 2918 96.83

[0063] As can be seen from the above, the compressive strength and drum index of the boron-magnesium pellets produced by this method are significantly better than those of conventional magnesium pellets.

[0064] The main chemical composition of the boron-magnesium pellets produced by this method is shown in Table 6.

[0065] Table 6 Comparison of Chemical Composition of Finished Balls (%)

[0066] Conventional magnesium pellets 66.13 0.96 0.22 1.27 2.62 0.29 0.85 0.006 0.027 Boron-magnesium pellets 65.27 0.89 0.21 1.28 2.87 0.33 1.02 0.005 0.033

[0067] As shown in the table above, the TFe grade of the boron-magnesium pellets produced by this method is slightly lower than that of conventional magnesium pellets, but the TFe grade still reaches 65.27%, and the content of harmful impurities S and P is low. With a similar MgO content, its strength index is significantly better than that of conventional magnesium pellets.

[0068] The metallurgical properties of the boron-containing magnesium pellets produced by this method compared with those of conventional magnesium pellets are shown in Table 7.

[0069] Table 7 Comparison of Metallurgical Properties of Finished Balls

[0070]

[0071]

[0072] As shown in Table 7, the boron-magnesium pellets produced by this method exhibit excellent metallurgical properties, with all indicators superior to those of conventional magnesium pellets. Its reducibility index reaches 70.52%, higher than the 70.09% of conventional magnesium pellets. This improvement in reducibility is attributed to the presence of boron (B) in the boron-magnesium-iron concentrate. 3+ With a small radius, it easily diffuses into the Fe2O3 crystal, causing lattice distortion and making Fe2O3 easier to reduce. The increase in the reduction index has a positive effect on blast furnace smelting production, especially on stabilizing and reducing the coke ratio. The reduction expansion rate of the boron-containing magnesium pellets produced by this method is only 10.43%, significantly lower than the 13.86% of conventional magnesium pellets. This indicates that the boron-containing magnesium pellets have good resistance to reduction expansion. The main reason is that magnesium ferrite is formed during the calcination process of the magnesium pellets. During the reduction of magnesium ferrite, the transformation from Fe2O3 to Fe3O4 does not occur; instead, a solid solution of FeO and MgO is formed, which inhibits the lattice expansion during the transformation from Fe2O3 to Fe3O4, thus improving the reduction expansion performance of the pellets. The low-temperature reduction pulverization index (RDI) of the magnesium pellets is also high. +3.15mm The reduction efficiency reached 99.67%, indicating that the boron-magnesium pellets exhibited good reduction strength. This is mainly due to two factors: firstly, the increased formation of olivine binder phase during the roasting process of the magnesium pellets with added boron-magnesium-iron concentrate plays a binding role during reduction, inhibiting pulverization; secondly, the magnesium-containing solid solution generated during the reduction of magnesium ferrite can suppress pellet pulverization, thus improving the reduction and pulverization performance of the pellets.

[0073] Through the above examples, the boron-containing magnesium pellets produced using this invention achieve a certain improvement in the quality of both green and finished pellets while ensuring pellet output. The boron-containing magnesium pellets produced by this invention have excellent chemical composition, low levels of harmful impurities, good metallurgical properties, and all indicators are superior to conventional magnesium pellets. Furthermore, the economical ore blending scheme and novel thermal operation process of this invention further reduce the production cost, equipment maintenance cost, and energy consumption of magnesium pellets, resulting in significant economic benefits and broad applicability.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications, equivalent substitutions, and improvements can be made without departing from the principles of this application, and all such modifications, substitutions, and improvements should be included within the protection scope of the present invention.

Claims

1. A method for preparing boron-containing magnesium pellets, characterized in that, include: S1. Preparation of mixture: Boron-magnesium-iron concentrate, red mud powder, grade 69 acid concentrate, and bentonite are mixed in a certain proportion to prepare the mixture; S2. Pretreatment of the mixture: Grinding the mixture; S3. Preparation of green pellets: First, water is added to the pretreated mixture, and then pellets are formed to obtain green pellets; S4. Preparation of finished pellets: The green pellets are first screened and dried in sequence, and then subjected to a low-temperature roasting thermal operation process. After preheating, low-temperature roasting, and finally cooling, boron-magnesium ore pellets are obtained.

2. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, The chemical composition of the boron-magnesium-iron concentrate is as follows: TFe content 52%–54%, SiO2 content 4%–5%, MgO content 10%–12%, B2O3 content 5%–6%, Ti content 0.01%–0.03%, and 70% of the particles have a 74μm particle size.

3. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, The chemical composition of the red mud powder is as follows: TFe content 45%–47%, SiO2 content 3%–4%, MgO content 0.1%–0.4%, Ti content 1.5%–2.5%, and 74μm particle size greater than 35%.

4. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, The chemical composition of the grade 69 acidic concentrate is as follows: TFe content 69.2%–69.8%, SiO2 content 1.5%–2.5%, MgO content 0.2%–0.4%, Ti content 0.3%–0.6%, and 74μm particle size greater than 95%.

5. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, In S1, the dry basis mass percentages of the mixture are as follows: 8%–9% boron-magnesium-iron concentrate, 3%–4% red mud powder, 86%–88% grade 69 acid concentrate, and 1%–2% bentonite.

6. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, In S2, the grinding includes one or more of ball milling, wet milling, and high-pressure roller milling.

7. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, In S4, the screening process involves screening out qualified green pellets of 8mm to 16mm size from the prepared green pellets and then feeding them into a chain grate machine for drying. The drying process involves controlling the temperature of the fume hood in the drying section of the chain grate machine between 100℃ and 550℃, with a temperature gradient of 50℃ / min, and a drying time of 9min to 10min.

8. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, In S4, the low-temperature roasting thermal operation process includes preheating and low-temperature roasting; wherein, the preheating is as follows: the dried green pellets enter the preheating section of the chain grate machine, the temperature of the preheating section is controlled at 600℃~1050℃, the temperature gradient is 50℃ / min, and the preheating time is 9min~10min.

9. The method for preparing boron-containing magnesium pellets according to claim 1, characterized in that, In S4, the low-temperature roasting process of the low-temperature roasting thermal operation is as follows: the pellets, after being dried and preheated by the chain grate machine, enter the rotary kiln for roasting, and a low-temperature roasting thermal operation system is adopted. The temperature in the rotary kiln is controlled at 1140℃~1190℃, and the roasting time is 25min~30min. The cooling process is as follows: the pellets are cooled in stages on the annular cooler until the temperature meets the requirements for storage or transportation.

10. A boron-magnesium-bearing pellet, characterized in that, It is obtained by the method for preparing boron-containing magnesium pellets according to any one of claims 1-9.

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